It's not a spoiler, but I'll bet -- something -- that it's none other than ALISTAIR HIMSELF.

Think about it: He hated Sheridan all that time because HE THOUGHT she was responsible for his beloved's death... but wait, what's this? She was ALIVE the whole time -- which means, after he found that out, he could stop torturing her. And after he could stop torturing her, he could focus on what he would have done all along with her: MOLDING HER INTO A TRUE CRANE! Hence, the attitude change, but still maintaining some of her old characteristics.